1. Field of the Invention
The present invention relates to a cathode composition for a lithium secondary battery, a process for producing the same, and a lithium secondary battery using the same.
2. Description of the Related Art
In recent years, portable information instruments, such as a personal computer, a portable telephone and an information terminal, have been widely used. Since these instruments have various multimedia functions, the secondary battery used for such instrument as power supply is demanded to be small and light having a large capacity, namely, to have a high energy density. In this regard, aqueous secondary batteries, such as a lead-acid battery and a nickel-cadmium battery conventionally used, are not sufficient. Lithium secondary batteries which can attain a higher energy density, especially the lithium secondary batteries using as a cathode active material, lithium composite oxide such as lithiated cobalt dioxide, lithiated nickel dioxide, and spinel lithium manganese oxide, and as an anode active material, a carbonaceous material that can be doped/undoped with lithium ions, have been developed.
Since these lithium secondary batteries have inherently a large energy, maximum safety against abnormalities, such as an internal short circuit and an external short circuit, is required. Although poly(vinylidene fluoride)(which may hereinafter be referred to as "PVDF") and vinylidene fluoride copolymer have been used as the binder of the cathode composition for lithium secondary batteries, further improvement of safety against an external heating is required.
When the suspension of polytetrafluoroethylene (which may hereinafter be referred to as "PTFE"), tetrafluoroethylene-hexafluoropropylene copolymer or tetrafluoroethylene-perfluoroalkylvinylether copolymer is independently used as a binder, the dispersibility of the resin is not good or the binding property with the current collector of a cathode is not sufficient.
In case that the dispersion medium is water using, as a binder, the suspension dispersed in water medium such as a PTFE suspension, there is a problem that the battery capacity drops by the deterioration of a cathode active material.